1. Field of the Invention
In at least one aspect, the present invention is related to methods of increasing the relative amounts of nitrogen and oxygen near the surface of a component made of a polymer.
2. Background Art
Surface-treatment technologies are of vital importance in the manufacturing industry for many applications that require materials specific surface properties. Surface modifications are used to improve chemical inertness, introduce surface cross-linking, increase surface conductivity, enhance dyeability, and most significantly, to improve adhesion.
Traditionally, adhesives are used in the automotive industry to attach windshields to vehicles. Historically, after application of either electrocoat or primer paint layer to the vehicle body, masking tape is applied to the windshield bonding flange area, and removed after basecoat/topcoat application. A solvent-based pinch-weld primer is then applied, and the windshield is adhered using a urethane adhesive. The taping and primer add material costs, and subsequent costs associated with either manual or machine labor. Additionally, the use of a solvent-based windshield adhesive primer in a plant is both an environmental and safety concern. Driven by cost reduction and design requirements, current efforts within the automobile industry are being aimed at achieving primerless windshield bonding to topcoat. This is being accomplished through modifications in paint and/or adhesive formulation chemistry to attain desirable bonding characteristics. Suppliers will ultimately cascade reformulation and verification costs into the cost of producing a vehicle, but savings realized through the elimination of taping and priming should offset this price. Moreover, substantial cost savings can be realized through primerless side glass bonding by elimination of the hardware necessary for attachment through “butyl-and-bolt”. Presently, primerless versions of DuPont Gen IV and Gen VI, PPG Carbamate, and BASF Ureclear are either used in production, or are soon scheduled for implementation. In the future, post-approval adjustments to topcoat formulation, which can be implemented to meet processing changes or cost reduction initiatives, would require a complete re-approval of the windshield bonding system to ensure that critical adhesive characteristics are maintained.
Most of the recent advances in clearcoat technology have been developed mainly for added resistance to effects of environmental etch and staining. To a large extent, this has been accomplished through modifications of bulk chemistry to remove functionality that is sensitive to the environmental factors causing etch. However, modifications of clearcoat formulation necessary to achieve primeness windshield bonding are accomplished either through incorporation of paint additives, or alterations to polymers that add bonding functionality to the topcoat surface. The consequence of these modifications is that environmental fallout could potentially bond more readily to this enhanced surface, resulting in appearance issues that could adversely affect customer satisfaction.
For glass bonding, good adhesion is essential only at the bonding flange. Thus alternatively, surface treatments of the topcoat, precisely in the bonding flange area, could potentially be utilized to enhance topcoat adhesion necessary to achieve primerless windshield bonding. This approach would not compromise the integrity of the entire painted vehicle surface. Similarly, a “universal” adhesive formulation that could bond to all topcoats would achieve this goal. However, the diversity in chemistries of topcoats available, added to the fact that formulation modifications can occur to paints during production over a period of time, makes the practicability of this later scenario unlikely.
Adhesion can be improved by increasing surface energy, increasing surface roughness, adding specific functional groups for specific interactions, or simply by removing weak boundary or contaminant layers that impede adhesion. For instance, surface treatments are being used to replace powerwash cleaning to remove mold release agents from plastic automotive headlamp lenses in order to facilitate bonding of a protective chip-resistance coating. In terms of bonding directly to coatings, surface treatments can eliminate the need for surface-active formulation additives to promote bonding, which potentially can interfere with fundamental processing issues relating to surface energy and wetability.
Some of the more common surface treatment technologies include UV radiation, ozone, corona discharge, flame, and low-pressure or vacuum plasma. Each method has certain advantages and disadvantages, depending upon the application. But plasma surface treatments are probably the most versatile, since they allow for the addition of different reactive gases that enable the construction of customized surfaces. Plasma surface treatments typically require a vacuum or low pressure for generation, which requires encapsulation of the entire object to be treated. Such spatial requirements limited the effectiveness of plasma treatments.
In a somewhat unrelated problem, each welded seam of an automobile body frame is overcoated with a sealant. During paint preprocessing, this sealant is observed to produce a residue that adheres to the various plastic automotive components during the various rinse cycles in the paint preprocessing. Such plastic parts components may optionally be coated with a paint prior to introduction of the vehicle body frame to the preprocessing steps. This phenomenon is typically referred to as sealant redeposition.
Accordingly, there exists a need for improved methods of adhering paint to a vehicle frame. Furthermore, there exists a need for a method of reducing sealant redeposition.